1. Field of the Invention
This invention relates to a turbo-compressor that has a housing and at least one rotor shaft supported in the housing. The rotor shaft has one free end, and a rotor connected to the other end. The rotor shaft is supported in the housing, for example in hydraulic or magnetic bearings, and preferably driven about its center, whereby it is possible to use high rom drives or other drive motors. The compressor can also be provided as a geared turbo-compressor that has a drive shaft with a toothed drive gear, and at least one rotor shaft driven by the drive gear. The drive shaft and the rotor shaft are pivotably supported in the gear housing the turbo-compressor. The rotor shaft has a rotor that is supported in an overhung manner.
2. The Prior Art
Due to the axial pressure differences occurring on the rotor, an axial thrust acts on the rotor shaft. Within the framework of known measures, this axial thrust is absorbed by a hydraulic axial bearing (see for example European Patent 0 008 616). In practical applications, the hydraulic axial bearing is often designed in the form of an axial, tilting segmented pressure bearing. The starting moment of the hydraulic axial bearing, which has to be overcome when the turbo-supercharger is started, is considerably high. For example, the high static friction of the stator has to be overcome first. The component of liquid friction occurring within the zone of mixed friction increases with the increase in peripheral speed, and the friction decreases to a minimum. As the number of revolutions increases further, the friction in the zone of liquid friction rises again, so that noticeable friction losses occur even at the rated rotational speed. These frictional losses are converted into heat that has to be dissipated by cooling. Moreover, a complicated and costly oil system with circulation is required to supply the hydraulic axial bearing.
The present invention provides an improved turbo-compressor with the structure described above, that effectively compensates for the axial thrust with the lowest possible loss, both during start-up and at the rated rotational speed.
To solve this problem, the invention provides that the free end of the rotor shaft, facing away from the rotor, projects into a pressure chamber connected with the housing, so that the free end of the shaft is acted upon by a pressurized fluid. The pressure exerted by the fluid acting on the free end of the rotor shaft compensates for the axial thrust acting on the rotor. The initial pressure acting on the rotor and the pressure of the fluid in the pressure chamber mounted on the free end of the shaft are balanced by means of control technology so as to completely compensate for the axial force acting on the rotor. An axial bearing supported on the housing, such as a hydrostatic sliding bearing is thus no longer required, even if the turbo-compressor is employed, for compressing fluids with high initial pressure. The structure of the gearing and the rotor housing are simplified due to the fact that a hydrostatic slide bearing is eliminated.
To guide the rotor shaft axially, butt rings or collars are preferably arranged on both sides of a driven section of the rotor shaft, the butt rings cooperating with the driving means to limit the axial thrust. In conjunction with a geared turbo-compressor, the butt rings are arranged on both sides of a pinion connected with the rotor shaft, and preferably have cooperating sliding rings to limit the axial thrust by engaging annular surfaces of a toothed drive gear mating with the pinion. This arrangement is possible since no high axial forces are transmitted.
The shaft passages at both ends of the rotor shaft need to be sealed. The shaft passage located at the free end of the rotor shaft preferably has a seal arrangement comprising at least one slide ring or similar seal to seal the pressure chamber. Particularly suitable is a seal arrangement comprising two sliding ring seals arranged one after the other, or similar seals, whereby a blocking medium or fluid can be admitted into the space between the seals. The same type of seal arrangement is recommended also to seal the shaft passage located at the front shaft end associated with the rotor. The shaft passages leading to the rotor and to the pressure chamber are preferably equipped with identical seal arrangements, which simplifies the stockkeeping of spare parts. The rotor shaft is preferably supported on radial slide bearings mounted within the housing.